In recent years, as an imaging apparatus for use in medical image diagnosis and non-destructive inspection using X rays, a radiation imaging apparatus using a flat panel detector (hereinafter referred to as an FPD) made of a semiconductor material has been put into practical use. The radiation imaging apparatus with an FPD is an apparatus capable of digital imaging by using the FPD to convert radiation, such as X-ray, transmitted through an object, such as a patient, to an analog electrical signal and converting the signal in analog/digital conversion to obtain a digital image signal. For example, in medical image diagnosis, such a radiation imaging apparatus with an FPD has been used as a digital imaging apparatus for still image radiographing such as radiography and moving image radiographing such as fluoroscopic imaging.
In order to use such an imaging apparatus in X-ray imaging, X-ray irradiation by an X-ray generating apparatus needs to be synchronized with operation of the imaging apparatus. Specifically, in response to the start of X-ray irradiation, the imaging apparatus needs to start the accumulation operation of accumulating electrical signals based on X-ray transmitted through the object. In response to the end of the X-ray irradiation, the imaging apparatus needs to start the read operation of reading the accumulated electrical signals.
Examples of the method of synchronizing the X-ray irradiation by the X-ray generating apparatus with the operation of the imaging apparatus include a method of using a cable to connect the X-ray generating apparatus to the imaging apparatus; and a method of causing the imaging apparatus to detect X-ray irradiation without a cable and starting the operation of the imaging apparatus in response to the detected X-ray irradiation.
As the method of detecting X-ray irradiation by the imaging apparatus, for example, there have been known techniques disclosed in the following Patent Literature 1 and Patent Literature 2. Patent Literature 1 describes a technique in which when X-ray irradiation is detected, neighboring pixel signals are added and the added signals are sequentially read. Patent Literature 2 describes a technique in which arbitrarily selected determination pixel signals are sequentially read to detect X-ray irradiation.